I recently took the test and here is my advice:
first and foremost: review your answers. Find the areas where u went wrong. and DONOT assume that it was just one question you got wrong in any particulararea . Accept that you are weak in that area. Gather notes, material, tricks, tips , a lotttt of fresh questions in each area and work on them. Spend time on each question. refer the material, find what was the point you missed in any problem and then solve next question keeping in mind the lesson you just learnt.

Also, do not study something and come back to it after many days. try to devote some time to each weak section everyday.
and when you are done with all that, take the first MGMAT test. If you do not get your desired score, start all over again. And you should not care much about the MGMAT score. You should care about how many questions you get wrong and why.

Thanks for the advice... Should i do everything again or focus only on my mistakes. I was thinking i should do my quant, verbal, og 11 and 12 again and then start tests.

I was always a weak maths student. Is the manhattan series good to learn basics.

I could gather that my weakness in verbal is sentence correction... what should i do to improve that.

you don't have to do this in all those areas. just focus on your weak areas. But don't forget to do at least 5-10 questions on your strong areas too.
This will help keep the concepts fresh in your mind and also boost your confidence.